It is well known that electrical machines require cooling to remove thermal energy which is generated in use. There are many electrical machines in which the only means of removing the power losses from coils and stator cores is via the back of the stator, usually into the main structural casing of the machine. Typically, such cooling methods include passing a fluid (i.e. a gas or liquid) coolant into the casing, such as a water jacket casing, or a void in the stator.
Regardless of the method used, the surface to volume ratio is an important factor in determining the level of cooling which is available and can become a limiting factor for the power density of the machine. This is particularly the case for machines in which casing materials with modest thermal conductivities, e.g. titanium, need to be used.
Hence, there exists a need to provide an effective way of removing heat from the core of a stator.
This general problem has been addressed in the prior art. For example, U.S. Pat. No. 5,331,238 describes a core retained within a housing in which a cooling fluid is supplied axially along an axis of the core between the housing and the core in order to cool the core. The core is described as having core laminations provided with cooling fins, and the core laminations may be rotated with respect to adjacent core laminations so that the cooling fins provide a cascaded cooling passage for the flow of the cooling fluid. A containment/growth sleeve is described as being inserted within or around the housing to minimize thermal deflection of the housing with respect to the core. Fluid conduits are provided in the housing which cooperate with the cascaded cooling passages.
GB2001481A describes an air-cooled electromotor having a stator including a plurality of laminations of non-circular external contour. The laminations are mutually offset in the direction of rotation of the rotor of the electromotor so that corners or projections of the laminations are exposed to cooling air and act as cooling fins for the stator.
US2007013241A describes a motor having a stator core disposed in a motor frame. The stator core is formed from a plurality of substantially identical laminations. Each lamination of the stator core comprises at least one recessed section, which, in cooperation with the frame, defines an incremental segment of closed passageway for routing a fluid along a perimetric surface of the stator core. Accordingly, the closed passageway provides a mechanism by which the outer regions of the stator core may be more effectively cooled. Furthermore, the laminations of the stator core may be oriented at varied orientations with respect to one another to form a labyrinthine path along the surface of the stator core through which coolant is routed.
U.S. Pat. No. 4,208,597 describes an arrangement for providing improved cooling for the end regions of the stator core of a large dynamoelectric machine in which a solid rigid vent plate is placed in contact with the finger plate at each end of the core. The vent plates are non-magnetic plates of the same configuration as the core laminations and have radial grooves in at least one surface. Coolant gas flows through the grooves to directly cool the finger plate and the end laminations of the stator core.
US2006284511 describes a motor having enhanced cooling. The exemplary motor includes a stator core formed from a plurality of stator laminations and a peripheral surface of the motor. Each stator lamination has a plurality of fins that extend radially outward. When assembled, the fins of adjacent laminations cooperate to form larger fins extending the length of the stator core. These fins enhance the cooling of the motor, by improving heat dissipation of the motor.
US2004012294A describes an electric motor, transformer or inductor having a lamination cooling system comprising a stack of laminations, each defining a plurality of apertures at least partially coincident with apertures of adjacent laminations. The apertures define a plurality of cooling-fluid passageways through the lamination stack, and gaps between the adjacent laminations are sealed to prevent a liquid cooling fluid in the passageways from escaping between the laminations. The gaps are described as being sealed by injecting a heat-cured sealant into the passageways, expelling excess sealant, and heat-curing the lamination stack. The apertures of each lamination can be coincident with the same-sized apertures of adjacent laminations to form straight passageways, or they can vary in size, shape and/or position to form non-axial passageways, angled passageways, bidirectional passageways, and manifold sections of passageways that connect a plurality of different passageway sections. Manifold members adjoin opposite ends of the lamination stack, and each is configured with one or more cavities to act as a manifold to adjacent passageway ends. Complex manifold arrangements can create bidirectional flow in a variety of patterns.
The present invention provides an improved arrangement for cooling a laminated stator of an electrical machine.